Cohabitation with a sick cage mate: consequences on behavior and on ehrlich tumor growth

[Touch, a crucial sense in social interactions to improve homeostasis in aging and promote healthy longevity]

Aging is associated with the generalized deterioration of the organism, being of great relevance experienced by homeostatic systems such as the nervous, immune, and endocrine systems, which increases the risk of morbidity and mortality. Among the lifestyle strategies that have been researched to improve these systems and achieve greater healthy longevity, this review will focus on the social environment. In order to verify the effectiveness of these both in the improvement of homeostasis and in life expectancy, the research carried out with experimental animals that have allowed this to be done will be discussed. In addition, as it has been observed that physical contact is crucial for the positive outcomes of social interaction on homeostatic systems and longevity to occur, we will focus on that mechanism, as well as some of the possible molecular pathways underlying the effects found.

[Improved immunity and mean lifespan in mature mice genetically deficient in catecholamine synthesis after living with wild type for two months]

INTRODUCTION

Mice hemizygous in tyrosine hydroxylase (TH-HZ), the limiting enzyme in catecholamine synthesis, show premature immunosenescence, which in females is associated with a shorter lifespan than the corresponding controls (WT). The coexistence of TH-Hz with WT improves the immune function in both males and females in adulthood.

OBJECTIVE

To test whether cohabitation for two months of mature male TH-HZ with WT improves the immune function of the former and whether this impacts the lifespan.

MATERIAL AND METHODS

Mature male ICR-CD1 mice (13 ± 1 months) TH-HZ coexisted with WT (2:4 ratio in each cage) for two months. Peritoneal leukocytes were extracted from all animals at baseline, one month, and two months after cohabitation, and macrophage phagocytic capacity, macrophage and lymphocyte chemotaxis, natural killer (NK) antitumor activity, and lymphoproliferative capacity in response to the mitogens concanavalin A and lipopolysaccharide (LPS) were assessed. The animals were maintained under these conditions until their natural death.

RESULTS

The TH-HZ, which start, in general, with lower values than the WT in the immune functions studied, improved them after two months of cohabitation, becoming similar to those of the controls. This improvement was already observed in NK activity after one month of cohabitation. The TH-HZ presented lower mean longevity than WT, but when they cohabited with WT, it was similar to the latter.

CONCLUSION

The coexistence of TH-HZ male mice with WT mice for two months at mature age improves these genetically modified animals' immune response and longevity.

What are the immune responses during the growth of Ehrlich's tumor in ascitic and solid form?

Traditionally, Ehrlich's tumor is used in experimental oncology to investigate the therapeutic capacity of different synthetic chemotherapeutic agents or to evaluate the antitumoral activity of different substances of natural origin. However, the understanding of immune mechanisms during Ehrlich carcinogenesis is still limited. In this review, we seek to describe the immune response during Ehrlich's tumor growth, and natural response without the influence of pharmacological administration, immunotherapies or concomitant challenges. The study followed the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). A systematic review was carried out that included experimental trials with mice challenged with Ehrlich's tumor. The research was carried out in three databases including MEDLINE/PubMed, Scopus, Latin American and Caribbean Literature in Health Sciences (LILACS). The searches resulted in 913 papers being found, of which 55 articles were considered eligible, and of these 55, 29 were selected for analysis. Findings indicate that there is an increase in the expression of M2 and T Helper (TH2) macrophages and of the cytokines IL-17, IL-1B, IL-6 and PGE in the ascitic form of Ehrlich. These phenotypic expressions are also found in ascitic neoplasms in humans. Ehrlich's solid tumor was characterized by increased expression of CD4, CD8, neutrophils and TNF-a, Foxp3 + and Qa-2 +, and these characteristics are analogous to human breasts cancers. It is our understanding that further studies are needed to assess the immune mechanisms in Ehrlich's tumor, since these findings can be used to improve cancer treatments that are analogous to Ehrlich's tumor.

Social Environment Ameliorates Behavioral and Immune Impairments in Tyrosine Hydroxylase Haploinsufficient Female Mice

The social environment can influence the functional capacity of nervous and immune systems, and consequently the state of health, especially in aged individuals. Adult female tyrosine hydroxylase haploinsufficient (TH-HZ) mice exhibit behavioral impairments, premature immunosenescence and oxidative- inflammatory stress. All these deteriorations are associated with a lower lifespan than wild type (WT) counterparts. The aim was to analyze whether the cohabitation with WT animals could revert or at least ameliorate the deterioration in the nervous and immune systems that female TH-HZ mice show at adult age. Female TH-HZ and WT mice at age of 3-4 weeks were divided into following groups: control TH-HZ (5 TH-HZ mice in the cage; TH-HZ100%), control WT (5 WT mice in the cage; WT100%), TH-HZ > 50% and WT < 50% (5 TH-HZ with 2 WT mice in each cage) as well as TH-HZ < 50% and WT > 50% (2 TH-HZ and 5 WT mice in each cage). At the age of 37-38 weeks, all mice were submitted to a battery of behavioral tests, evaluating sensorimotor abilities, exploratory capacities and anxiety-like behaviors. Subsequently, peritoneal leukocytes were extracted and several immune functions as well as oxidative and inflammatory stress parameters were analyzed. The results showed that the TH-HZ < 50% group had improved behavioral responses, especially anxiety-like behaviors, and the immunosenescence and oxidative stress of their peritoneal leukocytes were ameliorated. However, WT mice that cohabited with TH-HZ mice presented higher anxiety-like behaviors and deterioration in immune functions and in their inflammatory stress parameters. Thus, this social environment is capable of ameliorating the impairments associated with a haploinsufficiency of the th gene. Graphical Abstract.

The ratio of prematurely aging to non-prematurely aging mice cohabiting, conditions their behavior, immunity and lifespan

Adult prematurely aging mice (PAM) show behavioral deterioration, premature immunosenescence and increased oxidative stress, impairments that are associated with their shorter lifespan, compared to the corresponding exceptional non-prematurely aging mice (ENPAM). When PAM live in a predominantly ENPAM environment (2/5, respectively) they exhibit an improvement of immunity and redox state in their spleen and thymus leukocytes, and an increased lifespan. Nevertheless, it is unknown if other PAM/ENPAM ratios could affect behavioral and peritoneal leukocyte functions of PAM and change their lifespan. ENPAM and PAM were divided into the following groups: C-ENPAM (8 ENPAM in the cage); C-PAM (8 PAM in the cage); ENPAM>50% and PAM<50% (5 ENPAM/2 PAM in each cage); ENPAM = 50% and PAM = 50% (4 ENPAM/4 PAM in each cage), and PAM>50% and ENPAM<50% (5 PAM/2 ENPAM in each cage). After two months, mice were submitted to a battery of behavioral tests. Several functions and oxidative stress parameters were then assessed in their peritoneal leukocytes. Animals were maintained in these conditions to analyze their lifespan. The results showed that PAM>50%, PAM = 50% and PAM<50% exhibited better behavioral responses, immunity and redox states in their peritoneal leukocytes than C-PAM. This improvement was higher when the number of ENPAM in the cage was increased, with most of the parameters in PAM<50% reaching similar values to those in C-ENPAM, and an increased lifespan. However, ENPAM that cohabited with PAM showed, in general, an impairment of parameters studied. In conclusion, the PAM/ENPAM cohabitation ratio is relevant to behavior and immunity.

Odor cues released by Ehrlich tumor-bearing mice are aversive and induce psychological stress

BACKGROUND/AIMS

This study aimed to verify if odor cues released by Ehrlich tumor-bearing mice are aversive and stressful.

METHODS

Female mice were divided into a control group and an experimental group. One animal of each experimental pair of mice was inoculated with 5 × 10(6) Ehrlich tumor cells intraperitoneally; the other animal was kept undisturbed and was referred to as a CSP (companion of sick partner). One mouse of each control pair was treated intraperitoneally with 0.9% NaCl (1 mg/kg); the other animal (CHP, companion of healthy partner) was kept undisturbed.

RESULTS

It was shown that, in relation to CHP, CSP mice (1) spent less time within the companion zone in a T-maze place preference test, (2) had increased levels of social interaction, (3) had increased levels of plasmatic adrenaline and noradrenaline and (4) displayed no changes in serum corticosterone levels before and after an immobilization stress challenge. It was also shown that (5) cohabitation with 2 tumor-bearing mice was more effective in decreasing neutrophil oxidative burst than cohabitation with 1 sick partner and (6) the presence of a healthy conspecific within the cage of the tumor-injected/CSP pair abrogated the effects of cohabitation on neutrophil activity. These results show that odor cues released by Ehrlich tumor-injected mice are aversive and induce psychological stress.

CONCLUSION

We postulate that the aversive response induced by the chemosignals released by Ehrlich tumor-injected animals activates the sympathetic nervous system and causes the neuroimmunal changes that occur in the mice cohabiting with the sick mice.

Cohabitation with a sick partner increases allergic lung inflammatory response in mice

The bidirectional relationship between the nervous system and the immune system is relevant for homeostatic organism maintenance. Studies from our laboratory showed that 14days of cohabitation with a sick partner (injected with Ehrlich tumor cells-TAE) produced behavioral, neurochemical, endocrinological and immunological changes. This study analyzes the effects of cohabitation with an Ehrlich tumor-bearing animal on ovalbumin (OVA)-induced lung inflammatory response in mice. Pairs of male mice were divided into three groups: naïve, control and experimental. Animals of the naïve group were kept undisturbed being used for the assessment of basal parameters. One animal of each experimental and control pair of mice was immunized with OVA. On ED(0), these OVA-immunized animals received an OVA booster. At this day (D(0)) the experimental mice that were kept undisturbed were inoculated with 5×10(6) Ehrlich tumor cells; their immunized cage-mates were then referred as to CSP ("companion of sick partner"). The undisturbed mice of each control pair were i.p. treated on D(0) with 0.9% NaCl; their sensitized cage-mates were subsequently referred as CHP ("companion of health partner"). The OVA challenge was performed on CSP and CHP mice on ED(12) and ED(13); blood and tissue collection were performed on ED(14). Fourteen days after cohabitation, in comparison to the CHP mice, the CSP mice displayed the following: (1) an increased number of eosinophils and neutrophils in the BAL, (2) a decreased bone marrow cell count, (3) increased levels of IL-4 and IL-5 and decreased levels of IL-10 and IFN-γ in the BAL supernatant, (5) increased levels of IgG1-OVA, decreased levels of IgG2a-OVA and no changes in OVA-specific IgE in the peripheral blood, (6) increased expression of L-selectin in the BAL granulocytes, (7) decreased tracheal reactivity to methacholine measured in vitro, (8) no changes in plasma corticosterone levels and (9) increased levels of plasmatic noradrenaline. These results suggest that allergic lung inflammatory response exacerbation in CSP mice is a consequence of the psychological stress induced by forced cohabitation with the sick partner. Strong involvement of the sympathetic nervous system (SNS) through adrenaline and noradrenaline release and a shift of the Th1/Th2 cytokine profile toward a Th2 response were considered to be the mechanisms underlying the cell recruitment to the animal's airways.

The neuroimmune changes induced by cohabitation with an Ehrlich tumor-bearing cage mate rely on olfactory information

Cohabitation for 14 days with Ehrlich tumor-bearing mice was shown to increase locomotor activity, to decrease hypothalamic noradrenaline (NA) levels, to increase NA turnover and to decrease innate immune responses and decrease the animals' resistance to tumor growth. Cage mates of a B16F10 melanoma-bearer mice were also reported to show neuroimmune changes. Chemosignals released by Ehrlich tumor-bearing mice have been reported to be relevant for the neutrophil activity changes induced by cohabitation. The present experiment was designed to further analyze the effects of odor cues on neuroimmune changes induced by cohabitation with a sick cage mate. Specifically, the relevance of chemosignals released by an Ehrlich tumor-bearing mouse was assessed on the following: behavior (open-field and plus maze); hypothalamic NA levels and turnover; adrenaline (A) and NA plasmatic levels; and host resistance induced by tumor growth. To comply with such objectives, devices specifically constructed to analyze the influence of chemosignals released from tumor-bearing mice were employed. The results show that deprivation of odor cues released by Ehrlich tumor-bearing mice reversed the behavioral, neurochemical and immune changes induced by cohabitation. Mice use scents for intraspecies communication in many social contexts. Tumors produce volatile organic compounds released into the atmosphere through breath, sweat, and urine. Our results strongly suggest that volatile compounds released by Ehrlich tumor-injected mice are perceived by their conspecifics, inducing the neuroimmune changes reported for cohabitation with a sick companion.

Esquizofrenia: uma doença inflamatória?

OBJETIVO: Neste estudo, o objetivo foi revisar o papel de um possível processo inflamatório na gênese da esquizofrenia. MÉTODO: Foram selecionados os trabalhos publicados em revistas indexadas nas bases de dados Lilacs e MedLine, sob os unitermos "esquizofrenia", "inflamação" e "estresse oxidativo", nos últimos 10 anos até dezembro de 2009, nos idiomas inglês e português. Foram excluídos os artigos que tratavam de aspectos fisiopatológicos da doença fora do interesse da psiquiatria. RESULTADOS: Sessenta e um artigos foram selecionados. Doze abordavam o envolvimento do estresse oxidativo na esquizofrenia, nove tratavam de alterações no sistema imunológico de pacientes esquizofrênicos, dezesseis da infecção pré-natal como desencadeador da doença e sete mostravam a ação antioxidante e anti-inflamatória de fármacos antipsicóticos. CONCLUSÃO: Os estudos enfatizam o envolvimento do sistema imunológico (isto é, interleucinas e ação anti-inflamatória dos antipsicóticos), das infecções, do estresse oxidativo e da função mitocondrial na fisiopatologia da esquizofrenia. Portanto, esses novos achados são importantes para a melhor compreensão e, consequentemente, a elaboração de terapias mais específicas e eficazes no combate dessa doença mental.

Cohabitation with a B16F10 melanoma-bearer cage mate influences behavior and dendritic cell phenotype in mice

This study evaluated the effects of cohabitation with a B16F10 melanoma-bearer cage mate on behavior and immune functions in mice. Five different experiments were conducted. In each of them, the female mice were divided into two groups: control and experimental. One mouse of each control pair was kept undisturbed and called "companion of health partner" (CHP). One mouse of each experimental pair was inoculated with B16F10 cells and the other, the subject of this study, was called "companion sick partner" (CSP). On Day 20 of cohabitation, behavior and immune parameters from CHP and CSP mice were analyzed. In comparison to the CHP, the CSP mice: (1) presented an increased general locomotion in the open field and a decreased exploration time and number of entries in the plus-maze open arms; (2) had an enhanced expression of the CD80 costimulatory molecule on Iab(+)CD11c(+) spleen cells, but no differences were found on lymph nodes cells; (3) presented an altered differentiation of bone marrow cells in the presence of GM-CSF, IL-4, and LPS in vitro, resulting in a lower percentage of Iab(+)CD80(+) cells; (4) had a deficit in the establishment of a Delayed Type of Hypersensitivity to ovalbumin, which was associated to an in vitro proliferation of an IL-10-producing lymphocyte subpopulation after ovalbumin stimulation. Corticosterone levels detected on Day 20 of cohabitation were similar in CHP and CSP mice. It is shown here that DCs phenotype in mice is affected by conditions associated with behavioral alterations indicative of an anxiety-like state induced by the cohabitation with a tumor-bearer conspecific. This phenomenon occurred probably through a nondependent corticosterone mechanism.

Behavior: a relevant tool for brain-immune system interaction studies

Neuroimmunomodulation describes the field focused on understanding the mechanisms by which the central nervous system interacts with the immune system, potentially leading to changes in animal behavior. Nonetheless, not many articles dealing with neuroimmunomodulation employ behavior as an analytical endpoint. Even fewer papers deal with social status as a possible modifier of neuroimmune phenomena. In the described sets of experiments, we tackle both, using a paradigm of social dominance and subordination. We first review data on the effects of different ranks within a stable hierarchical relationship. Submissive mice in this condition display more anxiety-like behaviors, have decreased innate immunity, and show a decreased resistance to implantation and development of melanoma metastases in their lungs. This suggests that even in a stable, social, hierarchical rank, submissive animals may be subjected to higher levels of stress, with putative biological relevance to host susceptibility to disease. Second, we review data on how dominant and submissive mice respond differentially to lipopolysaccharide (LPS), employing a motivational perspective to sickness behavior. Dominant animals display decreased number and frequency in several aspects of behavior, particularly agonistic social interaction, that is, directed toward the submissive cage mate. This was not observed in submissive mice that maintained the required behavior expected by its dominant mate. Expression of sickness behavior relies on motivational reorganization of priorities, which are different along different social ranks, leading to diverse outcomes. We suggest that in vitro assessment of neuroimmune phenomena can only be understood based on the behavioral context in which they occur.

Chronic restraint stress impairs T-cell immunity and promotes tumor progression in mice

Long-term exposure to stressful situations can affect the immune system. The T-cell response is an important component of anti-tumoral immunity. Hence, impairment of the immune function induced by a chronic stressor has been postulated to alter the immunosurveillance of tumors, thus leading to a worse neoplastic prognosis. Here, we show that chronic restraint stress affects T-cell mediated immunity in mice. This was evidenced by a decrease of mitogen-induced T-cell proliferation, a reduction in CD4(+)T lymphocyte number and a decrease of tumor necrosis factor-alpha (TNF-alpha) and Interferon-gamma (IFN-gamma) production in stressed mice. Additionally, mice subjected to chronic restraint stress displayed an enhancement of tumor growth in a syngeneic lymphoma model, i.e. an increase of tumor proliferation and a reduction of animal survival. Finally, stressed mice had a reduced specific cytotoxic response against these tumor cells. These results suggest that chronic exposure to stress promotes cancer establishment and subsequent progression, probably by depressing T-cell mediated immunity. The T-cell immunity impairment as well as the tumor progression enhancement emphasize the importance of the therapeutic management of stress to improve the prognosis of cancer patients.

An animal model for the study of Chamomilla in stress and depression: pilot study

The behavioral and hematological effects of treatment with Chamomilla 6cH in mice subjected to experimental stress are described. Swiss mice were randomly divided into pairs, one animal was inoculated with Ehrlich's tumor, the other was treated daily with Chamomilla 6cH or control or received no treatment. After 7 days, the animals were observed in an open-field arena and blood samples taken. Mice who cohabitated with a sick cage-mate showed a decrease in their general activity, but those treated with Chamomilla 6cH were less severely affected (p=0.0426). No hematological changes were observed. In a second experiment, the forced swimming test was applied to mice pre-treated with Chamomilla 6cH, controls were: water, 10% ethanol or amitriptyline. Only the amitriptyline and ethanol treated groups showed significant excitatory behavior (p=0.0020), Chamomilla 6cH treated animals' scores intermediate between water control and ethanol or amitriptyline. A decrease in the leukocyte count was observed in the amitriptyline and Chamomilla 6cH treated groups (p=0.039). These data suggest that treatment with Chamomilla 6cH is related to the recovery of basal behavioral conditions in mice subjected to stressful conditions.

Neuroimunomodulação: sobre o diálogo entre os sistemas nervoso e imune

OBJETIVO: Trabalhos de pesquisa provenientes do campo da neuroimunomodulação vêm tornando explícitas as intrincadas relações existentes entre o sistema nervoso central e o sistema imune. Uma revisão bibliográfica foi realizada com o objetivo de descrever as bases de estudo da neuroimunomodulação. MODELOS EXPERIMENTAIS: Sabe-se, hoje, que estados emocionais como ansiedade e depressão são capazes de modificar a atividade do sistema imune como também o fazem o estresse e fármacos com ação no sistema nervoso central. COMPORTAMENTO DOENTIO: Os comportamentos apresentados por um organismo doente devem ser encarados como decorrência de estratégias homeostáticas de cada indivíduo. POSSÍVEIS MECANISMOS DE SINALIZAÇÃO DO SISTEMA IMUNE PARA O SISTEMA NERVOSO CENTRAL: Grande destaque tem sido atribuído para a participação do eixo hipotálamo-pituitária-adrenal, do sistema nervoso autônomo simpático e das citocinas nas sinalizações entre o sistema nervoso central e o sistema imune. CONCLUSÃO: O presente artigo pretende mostrar a relevância dos fenômenos de neuroimunomodulação; ele faz uma análise crítica das influências do sistema nervoso central sobre o sistema imune e vice-versa.

Social stress, immune functions and disease in rodents

The link between social factors, stress and health has been the focus of many interdisciplinary studies mostly because: (i) animals, including humans, often live in societies; (ii) positive and negative social relationships affect disease and well being; (iii) physiological alterations, which parallel social interactions also modulate immune and neuroendocrine functions. This review will focus on studies conducted on laboratory and wild rodents where social factors such as dyadic interactions, individual housing and differential group housing were investigated. The results obtained allow one to conclude that social factors in rodents are causally linked with immune disorders/disease susceptibility. In particular, lower lymphocyte proliferation and antigen-specific-IgG, granulocytosis and lymphopenia, as well as higher tumor induction and progression, are reliably associated with negative social events. Finally, due to the increasing utilization of social stress-based animal models the reliability of the concept of "social stress" and its evolutionary context are re-evaluated.

Cohabitation with a sick cage mate: effects on ascitic form of Ehrlich tumor growth and macrophage activity

The present study was designed to evaluate the effects of mice cohabitation with a sick conspecific cage mate on peritoneal macrophage activity and on resistance to Ehrlich tumor growth. Female mice housed in pairs were divided into control and experimental groups. One mouse of each control pair was inoculated with NaCl (0.1 ml/10 g) intraperitoneally and the other, called 'companion of healthy partner' (CHP), was kept undisturbed. One animal of each experimental pair of mice was inoculated with 5.0 x 10(6) Ehrlich tumor cells intraperitoneally and the other, the subject of this study, was called 'companion of sick partner' (CSP). Peritoneal macrophages were removed from CSP and CHP mice to analyze resident macrophage activity (experiment 1), macrophage activity after Mycobacterium bovis (experiment 2) or Ehrlich tumor cells (experiment 3) in vivo inoculations. The resistance of CSP and CHP mice to Ehrlich tumor growth was also analyzed (experiment 4). Differences between groups were not found on resident macrophage activity. However, Onco-BCG- and Ehrlich tumor-activated macrophages from CSP mice presented a decreased intensity and percentage of phagocytosis and an increased respiratory burst in the presence of Staphylococcus aureus stimulation in vitro. CSP animals at the same time displayed a decreased resistance to Ehrlich tumor growth. These data were discussed in light of a possible psychological stress effect imposed by the housing condition on mice's peritoneal macrophage activity and, as a consequence, on their resistance to Ehrlich tumor growth.

Cohabitation with a sick cage mate: Effects on noradrenaline turnover and neutrophil activity

The present study was designed to evaluate the effects of cohabitation for 11 days with a sick conspecific on hypothalamic levels and turnover of noradrenaline NA (experiment 1) and on neutrophil oxidative burst and phagocytosis in mice (experiment 2). Female mice were divided into two groups: control and experimental. One mouse of each control pair was kept undisturbed and called "companion of health partner" (CHP). One animal of each experimental pair of mice was inoculated with 5 x 10(6) Ehrlich tumor cells i.p., and the other, the subject of this study, was called "companion of sick partner" (CSP). In experiment 3, CHP and CSP mice were treated with diazepam (1.0 mg/kg) or with control solution (vehicle of diazepam, 1.0 mL/kg) 1h before evaluation of neutrophil activity. The CSP mice presented (1) decreased levels and increased turnover of hypothalamic NA; (2) decreased neutrophil oxidative burst after PMA or Staphylococcus aureus induction; (3) decreased percentage and intensity of neutrophil phagocytosis. In CSP mice, diazepam induced no changes in neutrophil oxidative burst or intensity of phagocytosis, but abolished almost completely the percentage of neutrophils performing phagocytosis. These data were discussed in the light of possible neuroimmune interactions.

Variations in behavior, innate immunity and host resistance to B16F10 melanoma growth in mice that present social stable hierarchical ranks

The present study analyzed the effect of social stable hierarchical dominance/submissive relationships in C57BL/6 mice on behavior, innate immunity, serum corticosterone levels and host resistance to B16F10 melanoma growth. Adult mice (90 days old) kept in pairs since weaning, were analyzed for dominant/submissive ranking in three consecutive days according to the presence or absence of fighting and/or anticipatory submissive responses. Only the pairs of mice where dominant/submissive relationships were clearly stated were employed. Results showed that submissive mice presented in relation to dominants: (1) decreased time spent in the central open-field area; (2) decreased number of entries into the open arms and decreased time spent in the exploration of the open arms of the plus maze; (3) increased time spent in exploration of the plus-maze closed arms; (4) decreased number of entries and in the time spent in the exploration of the third part of the plus-maze open arms; (5) increased number of B16F10 metastasis in the lungs; (6) decreased NK cell cytotoxicity measured in vitro in the peripheral blood and spleen; (7) decreased basal but not in S. aureus induced oxidative burst in both neutrophils and monocytes and (8) similar basal serum levels of corticosterone. The present behavioral findings show that submissive mice, within a stable social hierarchy, present anxiety like-responses a fact that would make than more prone to stressful stimuli. This condition would be responsible for the decreases presently observed on basal neutrophil oxidative burst, NK cell activity and resistance to B16F10 tumor growth. Together the obtained data show that mice that present stable hierarchical relationships display neuro-immune alterations comparable to those reported in mice under a situation of chronic social stress.